چکیده انگلیسی

Recent evidence suggests that a combination of shyness and sociability is associated with distinct behavioral and psychophysiological correlates at rest and in response to social stress and may be a risk factor for developmental psychopathology in children and illicit substance use in adolescents and young adults. Using the Cheek and Buss (1981) measurement model on the relative independence of shyness and sociability as a theoretical platform, we examined whether shyness and sociability were distinguishable on a measure of cerebral hemisphere dominance (i.e., a continuous measure of handedness) in young adults. We found a significant interaction between shyness and sociability on handedness. Undergraduates classified as high shy/high social had a higher degree of mixed-handedness compared with other combinations of shyness and sociability. Findings are discussed in terms of how mixed-handedness may reflect a lack of cerebral lateralization of some psychological processes important to the regulation of social behavior.

مقدمه انگلیسی

The search for personality correlates of handedness has a long and rich history in the normal and clinical adult personality literatures. Left-handed individuals have been found to be more anxious than right-handed individuals, and right-handed females have been found to be more extraverted than left-handed females (Hicks and Pellegrini, 1978 and Lester, 1987). Adults who are more right-hemisphere reliant (linked to left-handedness) have been found to have higher phobia scores than adults with a left-hemisphere style (Merckelbach, Muris, & de Jong, 1990). More recently, studies have suggested that left-handed individuals are more dominant, arrogant, calculating, and cold-hearted, and score lower on measures of nurturance than right-handed individuals (Coren, 1994).
The relation between personality and handedness has been of interest to clinicians as well. Moscovitch, Strauss, and Olds (1981) found that there was a complete absence of left-handers in a group of severely depressed patients undergoing electroconvulsive therapy (ECT). Conversely, Overby (1994) found a higher rate of non-right-handedness (left-handed or mixed-handedness) in a group of depressed females than in controls. Schizophrenia is another clinical disorder with strong links to handedness patterns. For example, patients with schizophrenia are known to have a higher rate of left-handedness compared with controls (Manoach, Maher, & Manschreck, 1988). This same study also found that all patients with schizophrenia who were left-handed had thought disorder, compared to 70% of right-handers, and that left-handers were more impaired than the non-left-handers. However, the relation between handedness patterns and individual differences in personality in normal and clinical populations is not a foregone conclusion.
For example, one study examining the relation between handedness and scores on Eysenck’s Personality Questionnaire failed to find significant results (Camposano, Corail, & Lolas, 1991). Another more recent study failed to find a relation between personality ratings and cerebral hemispheric lateralization, measured by hand, eye, and ear preference (Killgore, DellaPietra, & Casasanto, 1999). Still others have failed to find support for the notion of higher rates of fears and anxiety (Merckelbach, de Ruiter, & Olff, 1989) or psychosis (Overby, 1993) in normal adults. The lack of findings may be due to several issues: differences in the handedness measures used; a failure to consider another category of handedness: mixed-handedness, in which there is neither a strong right-hand preference, nor a strong left-hand preference (Giotakos, 2001); or perhaps a lack of theoretical models of personality in which testable hypotheses can be derived.
Research has consistently noted mixed-handedness patterns in individuals with schizotypal or psychosis-prone personalities (Chapman and Chapman, 1987, Claridge et al., 1998 and Kim et al., 1992). Specifically, it has been repeatedly shown that participant who score high on psychosis-proneness scales (e.g., the Perceptual Aberration Scale, the Magical Ideation Scale, the Impulsive Non-conformity Scale, and the Schizotypal Personality Questionnaire) have a higher incidence of mixed-handedness (Chapman and Chapman, 1987, Kim et al., 1992, Poreh, 1994 and Shaw et al., 2001). These patterns of results could be due, in part, to mild left hemisphere dysfunction, which would account for atypical handedness patterns and thought disorder common to schizotypal personality types (Kim et al., 1992). As well, an increase in mixed-handedness has been found in patients with borderline personality disorder, psychopathy, and mental retardation, while an increase in non-mixed-handedness (left or right-handedness) has been found in people with panic disorder (Giotakos, 2001 and Mayer and Kosson, 2000). It is reasonable to speculate then that mixed-handedness may reflect a cerebral organization in which a lack of hemisphere dominance develops, resulting in neither a strong left-hand preference, nor a strong right-hand preference. Moreover, this lack of hemisphere dominance and cerebral organization, given the personality handedness literature reviewed above, may predispose some individuals to particular personality styles and behaviors. The purpose of the present study was to examine mixed-handedness patterns in shyness and sociability in a group of undergraduates.
Some two decades ago, Cheek and Buss (1981) attempted to understand the origins of individual differences in shyness by considering how level of sociability interacted with shyness. Cheek and Buss noted that some people appear quiet and reserved in social situations. Cheek and Buss then asked: are these people reserved because they prefer to be alone rather than with others (i.e., they are introverts), or because they feel anxious and tense during social interactions, and these feelings inhibit their ability to act in such situations (i.e., they are shy)? Cheek and Buss developed short self-report measures to index shyness and sociability and selected participants who self-reported high and low shyness and sociability and observed them while interacting with unfamiliar peers. They found that high shy/high social (i.e., “socially conflicted”) undergraduates exhibited more overt behavioral anxiety during the social interaction compared with undergraduates in the other three groups.
In a series of studies using a design identical to that reported by Cheek and Buss (1981), we (Santesso et al., 2004, Schmidt, 1999, Schmidt and Fox, 1994 and Schmidt and Fox, 1995) examined the extent to which shyness and sociability were distinguishable on multiple behavioral and psychophysiological measures. We found that different combinations of shyness and sociability were distinguishable on resting frontal EEG alpha activity, two separate autonomic measures (mean heart rate and heart rate variability) just prior to an anticipated novel social encounter, and problematic behavior in young adults. Overall, undergraduates classified as high shy/high social exhibited a pattern of greater relative right frontal EEG activity at rest that was a function of heightened activity in both the left and right frontal region (Schmidt, 1999), a significantly faster and more stable heart rate in anticipation of a novel social interaction (Schmidt & Fox, 1994), and were more likely to engage in illicit substance use and substance use-related behaviors (Santesso et al., 2004) than young adults reporting other combinations of shyness and sociability. This latter finding on substance use correlates of shyness and sociability was also noted in adolescents (Page, 1990). Importantly, the Cheek and Buss (1981) measurement model concerning the relative independence of shyness and sociability has been independently replicated both with children (Asendorpf & Meier, 1993) and cross-culturally, in German (Czeschlik & Nurk, 1995) and Portuguese (Neto, 1996) translations.
We attempted to extend the Cheek and Buss (1981) measurement model by examining whether shyness and sociability were distinguishable on a continuous measure indexing cerebral hemisphere dominance (i.e., Edinburgh Handedness Inventory, Oldfield, 1971). It is possible that given the pattern of electrophysiological asymmetries noted in socially “conflicted” individuals, and the long and rich history noting a relation between handedness and personality, a continuous measure of hemispheric dominance may distinguish shyness and sociability. There appear to be, however, no studies examining whether shyness and sociability are distinguishable on continuous measures of handedness.